Grate bars showing some structural features for attaining a better permeability with respect to the traditional shape of bars, thus aiming at increasing the gas passage area, are already commercially known and used.
Generally, such conventional bars have rectangular profiles including only short radiuses for rounding the edges. Said conventional construction shows some shortcomings, among which we have the fact that, in the event of a downward gas flow, when it passes through the slot between the bars there is an abrupt expansion of the section that causes a whirling after the lower bar edges with the consequent energy loss.
Another shortcoming of said conventional construction is related to the fact that the mass of the bars causes a thermal loss when the bars leave the furnace outlet and return cold to the inlet thereof.
Another shortcoming of said conventional construction is related to the fact that the whirling and the passageway area limitation cause a load loss between 9 and 14% of the total load loss of the pellet bed plus the bars in the burning area.
On trying to minimize such problems, that is, to generate a higher permeability to the gas flow, studies have shown the importance of an improvement in the design of the grate bar, including a lower cost.
Within this expectation, there appeared a new sound proposal for a grate bar provided with spacers below the bar higher face (thus expanding the length of the slot) with just one central spacer having a higher width and therefore with a greater number of slots.